1. Field of the Invention
The present invention relates to a method of forming modified ground for the purpose of correcting soft grounds, forming foundations for buildings, supporting or holding a limited volume of ground, etc. and its device, and in particular, modified ground formation that can be carried out not only vertically but also horizontally as the main directions and at any angle to the land surface, namely the invention presents and modified ground formation method and a device therefor.
2. Description of the Prior Art
In the field of civil engineering, the development of forming modified ground is particularly urgent because civil engineering must cope with the age of the deepening extension of large cities underground, underground railways at deep underground levels, etc. which will undoubtedly occur soon. In civil engineering for underground works for large cities that sit on soft alluvium deposits, the success of these works depend on whether or not the reliable formation of modified ground is feasible. Various methods for forming an modified ground have been presented since the invention of the so-called CCP method (the trade mark--1970 by W. Nakanishi). More than a dozen new methods have been developed based on the CCP Method. All of them employ a modification of the discharge pressure, discharge volume, the use or non-use of air presented in the work method of the CCP Method, and their developments have all centered on a larger diameter of improved or modified ground. And, as mentioned above, we are now entering the age of large depth cities, large depth underground railways and city planning in bay areas which necessitate the need for a modified ground formation method which includes not only vertical works but also horizontal works, which have proved to be a challenge to the civil engineering industry.
In the prior art of forming an modified improved ground the so-called vertical work has been basic. With an increase in the pressure of the discharge, the quantity of discharge, and the volume of air used and other developments in this work, a large quantity of slurry is used, which causes higher ground pressure, making it more difficult for the adaptability of ground body formation which requires work at a large depth and on a horizontal level. For example, in an experiment on an actual work which was at a horizontal or oblique angle to the land face, the discharge of the slime from the gap around the injection rod stopped after about 4 minutes of starting the work, and soon some ground upheaval was noticed at the area of the work. Furthermore, after a few minutes the slime gushed out at an area distant from the work area. The result was, as shown in FIG. 15 (A), the formation of an irregular-shaped modified ground mass. This is considered to be caused by insufficient discharge of the slime against the amount of the injected slurry and also by the high pressure air mixed with the slime liquid which, being different from the case of a simple air mass, does not escape horizontally but tries to escape only upwards and remains in the ground as a volume of high pressure air, forming voids with the internal pressure that is gradually raised.
Also, in the stage of drilling a hole which procedes the formation of modified ground, conventional drilling machines provide no means for protection and the machine body, bit, etc. may be damaged because it is inserted into the ground and works there. When an injection rod is used for jetting a hardening agent, it must be equipped with a bit for drilling and the injection rod must be put into the hole as it drills. Alternatively, a device which combines an injection rod and a proper drilling rod as one body must be used. This precludes the use of a special device such as a pressure sensor, etc. at the tip end of the injection rod.
The present invention aims at correcting the disadvantages of the above mentioned work methods in the prior art and at the same time attempts to review the conventional modified ground formation methods from a systematic and general standpoint in order to contribute to the current industry of civil engineering.
An objective of the present invention is to provide an improved modified-ground body formation device which can be adapted to be used for not only soft ground but also hard ground and includes a drilling machine, which in practice will advance to a target point in the ground by drilling, and at the target point, the modified ground formation device will remove air and slime that attempts to remain, and to form a uniform and large diameter modified ground at any angle to the ground by keeping the slime pressure in the ground constant.
Another objective of the invention is to present a smooth slime discharge mechanism.
The method for forming modified ground which achieves these objectives will be called hereinafter in general `Metro-Jet System` (abbreviation, MJS--trade mark of the applicant of this invention).